Revised Abstract: The purpose of this core is to provide genetically modified animals, employing transgenic methodologies, for use in Projects 1-4. Mice will be obtained either via DNA infection of fertilized eggs or via injection of embryonic stem cells (ES cells) into blastocysts. The ES-cells carry targeted mutations obtained via homologous recombination. The core receives injection-ready DNA or ES-cells carrying targeted mutations from the different investigators and provide them with transgenic or chimeric mice for further breeding. In addition, the core will coordinate the injections and provide cell lines, guidance, and advice to investigators to ensure efficient generation of the transgenic strains.